Furnace with means for adjusting a crucible in growing crystals



3, 1966 J. J. COLEMAN ETAL 3,233,977

FURNACE WITH MEANS FOR ADJUSTING A CRUCIBLE IN GROWING CRYSTALS Filed May 51. 1961 2 fi$ .0 x

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WITNESSES INVENTORS Z Jacob J. Coleman Jozsef M. Feke're 8 WolterJ. Smith United States Patent 3,233,977 FURNACE Wl'llil MEANS FOR ADJUTING A CRUQHELE IN GROWING CRYSTALS Jacob J. Coleman, Braddock, Jozsef M. Fekete, Pittsburgh, and Walter J. Smith, Monroeville, Pa, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 31, 1961, Ser. No. 113,929 Claims. (Cl. 23273) The present invention relates generally to furnace apparatus and more particularly to furnace apparatus for the continuous growth of dendrite crystalline material.

In practicing the dendritic growth of semiconductor material in accordance with the aforementioned copending application, it has been noticed that the physical dimensions of dendrites, that is, width and thickness, are sensitive to variations in the relative position of the crucible to the heating means within the furnace chamber. lheir relative position determines the heat transfer therebetween and the distribution of heat to the supercooled mix contained by the crucible. Furthermore, if it is desired to pull a very long dendrite, some mechanism must be available to change the relationship between the melt and the heating means, since the melt surface is lowered as the dendrite is pulled.

The present invention discloses an apparatus by whic the crucible may be raised or lowered, and rotated when desired during the pulling of a dendrite. The apparatus allows very fine adjustments to be made, and actual use of the apparatus has shown these fine adjustments to be necessary for quality dendrite strips.

An object of the present invention is to provide apparatus for the fine control and adjustment of the physical dimensions of dendritic crystalline material as it is pulled from the melt.

Another object of the present invention is to provide apparatus for the raising, lowering and rotating of the crucible with respect to the heating means within a furnace.

Another object of the present invention is to provide apparatus for changing the relative position of the heating means and the crucible.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing, in which:

FIGURE 1 is an elevational view, partly in section, of a furnace embodying the present invention for the continuous growth of the dendrite strip; and

FIG. 2 is an enlarged cross-sectional view of the illustrative embodiment of the invention shown in FIG. 1.

As claimed and more fully described in the aforementioned copending application, the production of a continuous dendritic growth of crystalline material requires a furnace chamber 2 within which is mounted a crucible 4 on a support rod 6 of suitable material such as graphite. Heating means, illustrated as a coil 8, provide for heating and supercooling a melt contained within the crucible 4. A previously prepared crystal or seed of the material is brought in contact with the surface of the melt and slowly withdrawn thereby pulling after itself a portion of the melt which solidifies on the seed. Such a pulled strip is indicated at 10. Terminal connections to the heating means 8 are made through a packing gland 12 located in the wall of the furnace chamber 2.

In accordance with the present invention, adjustments are provided to allow the selection of the optimum thermal geometry for the initiation and continuation of proper dendritic growth as the melt surface is lowered.

Means are provided for rotating the crucible in a horizontal plane as well as moving the crucible up and down in the vertical plane. An auxiliary housing 20 is secured to an outer wall of the furnace chamber 2. A socket 22, supporting the graphite post 6 and crucible 4, extends into the furnace chamber 2 from the auxiliary housing 29. A piston member 24 having a central open ing 33 and capable of movement within the auxiliary chamber 20 supports the socket 22. Suit-able sealing means, such as O-rings 26, allow the movable piston 24 to slide within the auxiliary chamber 20 while maintaining a gas tight seal to the external atmosphere.

It is to be understood that the guiding means for directing the movable piston 24 need not require the use of the internal walls of the auxiliary housing and that any gas tight structure providing such a guiding means may be provided within the auxiliary chamber.

A long, narrow nut is fixedly secured in a groove within the auxiliary housing by means of bolts 31. The fixed nut 39 has a threaded opening 32 therethrough which is aligned with central opening 33. Actuating means, such as, a rod 34 is threaded through the opening 32 and is rotatably mounted on said movable piston 24 by means of ring members 36 and 38 which abut shoulders on the top and bottom portions, respectively, of the center portion 33 of the movable piston 24. To actuate the threaded rod 34 thereby advancing and retracting the piston member 24, and hence the crucible 4 relative to the heating coils 8, a ratchet crank 38 is secured at one end of the threaded rod 34. Sealing means in the form of a packing ring 40 maintain the gas tight seal between the furnace and outer atmosphere. Suitable openings 37, to provide the necessary space for the nut 30, are formed within the piston 24 to allow it to move within the auxiliary housing 20 within prescribed limits.

In order to impart rotation of the movable piston in a horizontal plane, a handle is secured to the movable piston 24. A guide member 52 is secured to a ring 54 keyed into the groove 53 in the outer wall of the auxiliary housing. The guide member 52 extends from the auxiliary chamber and through the handle 50 by means of the opening collar 56. Rotation of the handle St) in a horizontal plane will accordingly rotate the movable piston 24 through approximately with the rod 34 being the axis of such rotation. The ring 54 seated in the outer circumference of the housing is adapted to rotate with the piston and at the same time insure that the piston will not be forced out of alignment with the internal walls of the auxiliary housing.

It is to be noted that upon rotation of the ratchet crank 38 thereby advancing or retracting the crucible within the furnace chamber that the guide member 52 allows the handle 50 to advance and retract along with the movable piston 2-4. Should, however, rotation be desired in the horizontal plane, the handle 50 can cause such rotation since the guide member 52. is secured to the ring 54 seated in the groove 53 in the outer circumference of the auxiliary chamber and will therefore rotate with the handle 50. The ring 54 is rotatable within the groove 53 formed in the outer circumference of the auxiliary housing.

When it is desirable to prohibit rotation of the movable piston 24 and hence the crucible 4, the movable piston 24 may be locked in position Within the auxiliary housing by means of the set screw 58 which will clamp the ring 54 to the auxiliary housing 20.

The adjustments provided by the present invention allow the altering of the physical dimensions, thickness and width, of a dendrite during its pulling, since the adjustments result in changes of the thermal geometry of the crucible and melt system. These adjustments allow the selection of the optimum thermal geometry for the initiation and continuation of dendritic growth.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications, alterations and substitutions within the spirit and scope of the present invention are herein meant to be included. For instance, the relative vertical motion desired between the crucible and the heating means can be as readily accomplished by moving the coil rather than the crucible, or dividing such movement between each. The thermal geometry can be further altered by suitable introduction or removal of heating shields within the furnace chamber 2. Variation of the amount of power supplied to different parts of the crucible may also be provided. While the coil 8 has been illustrated and suggested to be of radio frequency heating variety, other methods of heating are possible.

We claim as our invention:

1. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of dendritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining an air tight seal therebetween; actuating means rotatably mounted on said piston member and cooperating with said auxiliary housing to effect movement of said piston member vertically relative to said auxiliary housing; said crucible adapted to move with said piston member relative to said heating means.

2. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of dentritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining an air tight seal therebetween; said piston member having an opening therethrough and a shoulder on each side of said opening; actuating means extending through said opening and having a first ring member and a second ring member engaging a shoulder on each side respectively whereby said piston member is held captive thereinbetween; said actuating means cooperating with said auxiliary housing for effecting movement of said piston member vertically relative to said auxiliary housing; and said crucible adapted to move with said piston member relative to said heating means.

3. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of'dendritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; said piston member having an opening therethrough; actuating means extending through said opening and coupled to said piston member for actuating movement of said piston member relative to said auxiliary housing; said crucible adapted to move with said piston member vertically relative to said heating means.

4. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of dendritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; means coupled to said piston member for actuating movement of said piston member vertically relative to said auxiliary housing; said crucible adapted to move with said piston member relative to said heating means.

5. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of dendritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; a rod member rotatably mounted on said piston member and coupled to said piston member to effect axial movement of said piston member relative to said rod member; said piston member having a central opening therethrough; a nut member secured to said auxiliary housing and having a threaded opening aligned with said central opening; said rod member extending through said central opening and threaded through said threaded opening; said crucible adapted to move with said piston member relative to said heating means.

6. Apparatus for controlling the relative position of components within a furnace including a crucible and heating means for the continuous growth of dendritic crystalline material; said apparatus comprising, an auxiliary housing securable to said furnace; a piston member adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; a rod member rotatably mounted on said piston member and coupled to said piston member to effect axial movement of said piston member relative to said rod member; said piston member having a central opening therethrough; a nut member secured to said auxiliary housing and having a threaded opening aligned with said central opening; said rod member extending through said central opening and threaded through said threaded opening; said crucible adapted to move with said piston member relative to said heating means, means for rotating said piston member within said auxiliary housing; said piston member including a handle secured to said piston member; a guide member extending from said auxiliary housing and through said handle; said handle adapted to cooperate with said guide member for rotation of said piston member about said rod member; and a ring seated in the outer circumference surface of said housing adapted to rotate with said piston upon movement of said handle whereby said piston will readily rotate without tilting within the inner walls of said auxiliary housing.

7. Apparatus for controlling the relative position of a crucible to a heating means within a furnace chamber comprising, in combination; an auxiliary housing secured to said chamber; a piston adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; a connecting rod engaging said crucible and extending from said chamber into said auxiliary housing; means operably connected to the connecting rod for moving said crucible in a vertical motion; and second means for rotating said crucible in a horizontal plane.

8. Apparatus for controlling the relative position of the crucible to a heating means within a furnace chamber comprising, in combination; an auxiliary housing secured to said chamber; a piston member adapted to slide within said auxiliary housing while maintaining a gas tight seal therebetween; a rod secured to said piston member and extending from said auxilary housing into said chamber; said rod threaded to move vertically relative to said auxiliary housing and the furnace chamber; said crucible secured to said rod and adapted to change its position relative to said heating means when the threaded rod is moved relative to said auxiliary housing.

9. Apparatus for controlling the relative position of the crucible to a heating means within a furnace chamber comprising, in combination; an auxiliary housing secured to said chamber; a piston member adapted to slide within said auxiliary housing While maintaining a gas tight seal therebetween; a rod secured to said piston member and extending from said auxiliary housing into said chamber; said rod threaded to move vertically relative to said auxiliary housing and the furnace chamber; said housing including a threaded opening fixedly secured with respect to said housing and chamber; said piston member adapted to move vertically with respect to said housing by advancing and retracting through said threaded opening whereby its relative position is altered with respect to the housing and said heating means; said crucible adapted to move with said piston member.

10. Apparatus for adjusting the thermal geometry of a crucible with respect to heating means within a furnace chamber; said apparatus comprising a slidable mount for said crucible; a housing for said slidable mount; said housing including a threaded nut rigidly secured to said 1 housing; a threaded rod extending through said nut and engaging said crucible to impart vertical motion thereto as the rod is rotated with respect to the threaded nut.

References Cited by the Examiner UNITED STATES PATENTS 1,498,638 9/1922 Periolat 269-47 1,609,282 12/1926 Ash 269-50 X 2,747,971 5/1956 Heill 23-301 2,872,299 2/1959 Celmer et a1. 23-301 X 2,905,798 9/1959 Freutel 23- 301 2,914,397 11/1959 Sterling 148-1.5 X 2,979,386 4/1961 Shockley 23-301 X 10 3,086,850 4/1963 Mauno 23-301 OTHER REFERENCES Zone Melting, by Pfann, pages 70 to 71, John Wiley and 5 Sons Inc., Chapman and Hall.

NORMAN YUDKOFF, Primary Examiner. MAURICE BRINDISI, Examiner. 

1. APPARATUS FOR CONTROLLING THE RELATIVE POSITION OF COMPONENTS WITHIN A FURNACE INCLUDING A CRUCIBLE AND HEATING MEANS FOR THE CONTINUOUS GROWTH OF DENDRITIC CRYSTALLINE MATERIAL; SAID APPARATUS COMPRISING, AN AUXILIARY HOUSING SECURABLE TO SAID FURNACE; A PISTON MEMBER ADAPTED TO SLIDE WITHIN SAID AUXILIARY HOUSING WHILE MAINTAINING AN AIR TIGHT SEAL THEREBETWEEN; ACTUATING MEANS ROTATABLY MOUNTED ON SAID PISTONG MEMBER AND COOERATING WITH SAID AUXILIARY HOUSING TO EFFECT MOVEMENT OF SAID PISTON MEMBER VERTICALLY RELATIVE TO SAID AUXILIARY HOUSING; SAID CRUCIBLE ADAPTED TO MOVE WITH SAID PISTON MEMBER RELATIVE TO SAID HEATING MEANS. 